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This photo provided by the Iowa State Patrol shows the scene of a 25-vehicle pileup that killed two people and injured several others Thursday, Dec. 20, 2012 on Interstate 35 about 60 miles north of Des Moines, Iowa. Authorities say poor visibility caused the accident when drivers were unable to see vehicles that had slowed or stopped, causing a chain reaction of crashes. (AP Photo/Iowa State Patrol)

This photo provided by the Iowa State Patrol shows the scene of a 25-vehicle pileup that killed two people and injured several others Thursday, Dec. 20, 2012 on Interstate 35 about 60 miles north of Des Moines, Iowa. Authorities say poor visibility caused the accident when drivers were unable to see vehicles that had slowed or stopped, causing a chain reaction of crashes. (AP Photo/Iowa State Patrol)